In a hydrometallurgical method for a nickel oxide ore, for example, a solution obtained by neutralizing a leachate of a nickel oxide ore or a solution for nickel recovery from which impurities have been removed is sulfurized by blowing hydrogen sulfide gas thereto to form a metal sulfide.
The hydrogen sulfide gas used at this time is produced in a hydrogen sulfide gas production plant configured as shown in FIG. 3 or FIG. 4, for example.
Specifically, the hydrogen sulfide gas production plant 50 shown in FIG. 3 includes a reaction facility 51 that generates hydrogen sulfide gas from supplied sulfur and hydrogen gas, a cooling facility 52 that cools the hydrogen sulfide gas, a cleaning facility 53 that cleans sulfur contained in the hydrogen sulfide gas, and a drying facility 54 that dries the cleaned hydrogen sulfide gas to remove moisture. In addition, the hydrogen sulfide gas production plant 50 is provided with, as incidental facilities, a storage facility 55 that stores the generated hydrogen sulfide gas and a supply facility 56 that supplies the hydrogen sulfide gas.
In the hydrogen sulfide gas production plant 50, a catalyst is used in the reactor 51 for the purpose of reducing the activation energy. In addition, in the hydrogen sulfide gas production plant 50, after sulfur contained in the produced hydrogen sulfide gas is removed in the cleaning facility 53, moisture is removed in the drying facility 54, thereby preventing the corrosion of the facilities due to moisture.
In addition, in the hydrogen sulfide gas production plant 50, the produced hydrogen sulfide gas is compressed to a necessary pressure using the supply facility 56, such as a compressor, and the compressed hydrogen sulfide gas is supplied to a plant that uses hydrogen sulfide gas in the dezincification process, the sulfurization process, or the like in the hydrometallurgical method for a nickel oxide ore mentioned above, for example.
In the hydrogen sulfide gas production plant 50, as conditions for the production of hydrogen sulfide gas, for example, the plant is operated at a pressure of about 5 kPaG and a temperature of about 380° C. In this hydrogen sulfide gas production plant 50, a catalyst is used in the reaction facility 51. Therefore, the plant can be operated at low-pressure and low-temperature conditions, and this has been an advantage in operation.
However, in the hydrogen sulfide gas production plant 50, it is necessary to regularly exchange the catalyst in the reaction facility 51. In addition, considering the catalyst life, it is necessary to strictly control the quality of sulfur, which is a raw material for hydrogen sulfide gas.
Meanwhile, the hydrogen sulfide gas production plant 60 shown in FIG. 4 is a plant that does not use a catalyst in a reactor. As shown in FIG. 4, the hydrogen sulfide gas production plant 60 includes a reaction facility (a reactor 66, a quench tower 67, a heater 68) 61 that generates hydrogen sulfide gas from sulfur and hydrogen gas, cooling facilities 62 (62A, 62B) that cool the hydrogen sulfide gas, a knockout facility 63 that removes sulfur in the hydrogen sulfide gas and supplies the hydrogen sulfide gas, and a blowdown facility 64 that recovers the sulfur removed from the hydrogen sulfide gas and supplies the same to a sulfur processing plant or the like. In addition, the hydrogen sulfide gas production plant 60 is provided with, as an incidental facility, a facility 65 that cools the temperature of sulfur to adjust the heat balance.
In the hydrogen sulfide gas production plant 60, molten sulfur is stored in the reactor 66 of the reaction facility 61, and hydrogen gas is supplied from the lower part. Accordingly, while the hydrogen gas passes through the molten sulfur, a hydrogen sulfide gas generation reaction proceeds. Incidentally, sulfur, which decreases due to the reaction, is supplied from the upper part of the reaction facility 61. The hydrogen sulfide gas generated in the reaction facility 61 is mostly hydrogen sulfide, but contains sulfur steam involved when the hydrogen gas passed through the reactor.
In addition, as the conditions for the production of hydrogen sulfide gas, the hydrogen sulfide gas production plant 60 is operated under high-temperature and high-pressure conditions such as, for example, a pressure of about 800 kPaG and a temperature of about 470° C. The temperature of the generated hydrogen sulfide gas is reduced to about 150° C. when discharged from the quench tower 67 forming the reaction facility 61. The hydrogen sulfide gas is further cooled in the cooling facility 62 to about 50° C. (temperature for use in the facility of the supply destination) and then transferred to the knockout facility 63.
In addition, most of sulfur contained in the hydrogen sulfide gas generated in the reaction facility 61 causes serious problems in operation when it adheres to valves, such as a control valve and a manual valve, or meters, such as a thermometer and a pressure meter, in a plant that uses hydrogen sulfide gas, for example, which is the supply destination. Therefore, sulfur is once solidified in the knockout facility 63, and the sulfur accumulated at the bottom is heated by steam through a jacket installed on the lower outer periphery of the knockout facility 63, thus melted, and recovered. The recovered sulfur is stored in the blowdown facility 64, then supplied to a sulfur processing plant using a supply pump 69, and thus processed or repeatedly used.
In this way, sulfur contained in the hydrogen sulfide gas generated in the hydrogen sulfide gas production plant 60 is separated by a knockout drum, and the hydrogen sulfide gas is then supplied to a plant that uses hydrogen sulfide gas in the dezincification process, the sulfurization process, or the like in the hydrometallurgical method for a nickel oxide ore mentioned above, for example.
In the hydrogen sulfide gas production plant 60, the operation control is performed in the state where the pressure in the system is high. Accordingly, facilities such as a compressor and a chiller facility are not necessary, whereby the initial investment can be held down. Further, unlike the hydrogen sulfide gas production plant 50 mentioned above, the regular catalyst exchange, the exchange cost therefor, and the cost of maintenance including sulfur quality control are unnecessary, leading to an advantage in that the operation cost can be reduced.
However, because the hydrogen sulfide gas production plant 60 is operated under high-pressure and high-temperature conditions, when the produced hydrogen sulfide gas is to be supplied, it is necessary to reduce the pressure to a pressure suitable for the operation of the plant of the supply destination. For example, in a plant for the sulfurization process in which a nickel oxide ore is processed to form a mixed sulfide containing nickel and cobalt (mixed sulfide: MS), the plant is operated with the pressure of hydrogen sulfide gas being about 350 kPaG. In addition, in a plant for the dezincification process in which sulfurization is performed to convert zinc contained in the neutralization end solution into zinc sulfide, the plant is operated with the pressure of hydrogen sulfide gas being about 5 kPaG or less. In addition, in the hydrogen sulfide gas production plant 60, because the plant is operated under high-pressure and high-temperature conditions, the risk in case of gas leakage is high, and there is an increased load on the hydrogen sulfide gas cooling facility 62, which is a facility that cools sulfur (sulfur steam) contained in the hydrogen sulfide gas, or the knockout facility 63, which is a facility that recovers the hydrogen sulfide gas.
In addition, in the hydrogen sulfide gas production plant 60, although sulfur contained in the generated hydrogen sulfide gas is recovered and removed in the knockout facility 63, some of the sulfur solidifies in the cooling facility 62 and adheres to the inside, which reduces the operation efficiency when allowed to stand as it is. Therefore, a plurality of cooling facilities are provided, and they are switched and used alternately.
Specifically, for example, two systems of cooling facilities 62A, 62B are provided, and, with a decrease in the cooling capacity due to sulfur adhering to the inside, the cooling facility 62A in use (facility having adhesion inside) is switched with the standby cooling facility 62B (facility with the adhesion inside being removed). Then, with respect to the cooling facility 62 whose cooling capacity has decreased, the sulfur adhering in the facility is melted using steam and recovered, thereby making it standby. By repeating these operations, the hydrogen sulfide gas production plant 60 is prevented from a decrease in the operation rate. Incidentally, the sulfur melted and recovered in the cooling facility 62 (62A, 62B) is transferred to the blowdown facility 64 and processed in the same manner.
Incidentally, in the hydrogen sulfide gas production plant 60, the hydrogen sulfide gas production facilities are operated under high-pressure and high-temperature conditions as mentioned above. Accordingly, it is believed that trouble is likely to occur, including problems in each control valve or ON/OFF valve and problems in each meter, as well as leakage of hydrogen sulfide gas from the hydrogen sulfide gas production facility or incidental facilities, pipe clogging due to the adhesion of sulfur contained in hydrogen sulfide gas or the like.
In order to prevent such trouble beforehand, regular inspections on the hydrogen sulfide gas production plant are necessary.
In case of trouble as above or at the time of regular inspection, it is necessary that the hydrogen sulfide gas production plant and the processing plant that uses hydrogen sulfide gas are isolated by an ON/OFF valve or the like, and then the inside of the hydrogen sulfide gas production plant is replaced with nitrogen gas. In addition, also in the case where a problem occurs in the processing plant that uses hydrogen sulfide gas, it is necessary that the hydrogen sulfide gas production plant and the processing plant that uses hydrogen sulfide gas are isolated by an ON/OFF valve or the like, before dealing with the problem.
Accordingly, in case of trouble or at the time of regular inspection, low-concentration hydrogen sulfide gas will be present in the plant.
Further, when hydrogen sulfide gas is to be produced, it is necessary to replace the hydrogen sulfide gas production facility and its incidental facilities with a nitrogen gas atmosphere in advance of the start-up. Therefore, at the time when the operation has just started and hydrogen sulfide gas has been just generated (produced), the concentration of the hydrogen sulfide gas is low, and it is necessary to take a measure also in the processing plant that uses hydrogen sulfide gas, such as the adjustment of the flow rate.
Usually, such low-concentration hydrogen sulfide gas is a loss as so-called waste hydrogen sulfide gas. Such waste hydrogen sulfide gas is extremely toxic and cannot be discharged into the air as it is. Therefore, the gas has to be processed in a flaring facility (facility that causes combustion to reduce toxicity) or a harm elimination facility using caustic soda or the like, before discharge.
However, in the case of processing in a flaring facility, the hydrogen sulfide gas turns into SOx gas and, though only slightly, affects the environment. Meanwhile, in order to make it harmless by a harm elimination facility, a neutralizing agent such as caustic soda is required. Such a neutralizing agent has to be taken into consideration as operation cost, resulting in a decrease in the efficiency of operation.
Therefore, there has been a demand for a method for recovering and effectively using such low-concentration hydrogen sulfide gas.
For example, Patent Literature 1 proposes, as a method for recovering an excess of hydrogen sulfide gas discharged from a sulfurization reaction tank in the sulfurization (nickel recovery) process in which a nickel oxide ore is processed to produce MS, a method in which the hydrogen sulfide gas is returned to the process through a solution prepared by absorption in caustic soda (in the form of sodium hydrogen sulfide, sodium sulfide or the like), and the sulfur content is used for the sulfurization reaction.
In addition, Patent Literature 2 discloses a method in which hydrogen sulfide gas vaporized during the dehydration process is absorbed by an organic amide solvent and thus recovered out of the system where the dehydration process is performed, and the recovered hydrogen sulfide is reused as a raw material of an alkali metal sulfide for a polymerization reaction.
However, these methods do not recover hydrogen sulfide as gas, and also recovering solvents, such as caustic soda and organic amide, are necessary.
Patent Literature 3 discloses, in a method in which an aqueous sulfuric acid solution containing nickel and cobalt is introduced, and also a gas for sulfurization containing hydrogen sulfide is supplied to the gas phase, thereby producing a sulfide containing nickel and cobalt, a method for maintaining the high yield of nickel and cobalt in the case where the hydrogen sulfide gas concentration in the sulfurization gas supplied into the reaction vessel decreases from 95 to 100% by volume used in the steady state of operation to a lower concentration. Specifically, according to the method, in the case where the hydrogen sulfide gas concentration is 85 to 90% by volume, the input of nickel and cobalt introduced into the reaction vessel is 30 to 35% by mass of the input in the steady state, while in the case where the hydrogen gas concentration is more than 90% by volume, the input of nickel and cobalt introduced into the reaction vessel is reduced to 55 to 60% by mass.
This method makes it possible to effectively use the hydrogen sulfide gas having a lower concentration than in the steady state. However, the method cannot deal with the case where the inside of the hydrogen sulfide gas production plant is replaced with nitrogen, and the hydrogen sulfide gas concentration decreases to less than 85% by volume, for example.